As the sunlight passes through the atmosphere, the rays are scattered by tiny particles of dust, pollen, soot and other minute particulate matters present there. However, when we look up, the sky appears blue during mid-day, because

The blue appearance of the sky during mid-day is primarily due to Rayleigh scattering. Sunlight consists of various wavelengths, and as it passes through the atmosphere, it interacts with air molecules and fine particles [c1][t1]. These particles are smaller than the wavelength of visible light, making them more effective at scattering shorter wavelengths (blue end) than longer wavelengths (red end) [c1][t2]. Blue light travels in shorter, smaller waves and is scattered in all directions by the gases and particles in the air [t1][t5]. Consequently, when we look up during the day, our eyes perceive this scattered blue light coming from all parts of the sky [c1][t2]. While violet light has an even shorter wavelength, the sky appears blue because the sun emits more blue light and the human eye is more sensitive to blue [t2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.6.2 Why is the colour of the clear Sky Blue? > p. 169
2. [2] https://spaceplace.nasa.gov/blue-sky/